High-strength silicon steel

ABSTRACT

A HIGH-STRENGTH SILICON STEEL CONSISTING OF LESS THAN 0.03% C, 4-6% SI, 5-10% NI, 6-18% CR, LESS THAN 4% EACH OF MN, MO AND CU, LESS THAN 2% V AND RESIDUE ESSENTIALLY FE, IN WHICH THE TOTAL AMOUNT OF NI AND MN IS VARIED SO AS TO APPROACH 2 TIMES THE SI CONTENT AND THE CR VARIED ABOUT 2.5 TIMES TO THE SI CONTENT, SO THAT THE AC3 TRANSFORMATION POINT IS LOWERED TO LESS THAN 1400*F.

United States Patent 3,674,468 HIGH-STRENGTH SILICON STEEL Keiichi Ota,54 Nakagawara-cho, Sakyo-ku,

Kyoto, Japan I No Drawing. Continuation-impart of application Ser. No.708,530, Feb. 27, 1968. This application Nov. 23, 1970, Ser. No. 92,144

Int. Cl. C22c 39/20, 39/44 U.s. cl. 7s-'-12s A 4 Claims ABSTRACT OF THEDISCLOSURE CROSS REFERENCES This application is a continuation-in-partof copending application, Ser. No. 708,530 filed Feb. 27, 1968 and nowabandoned.

BACKGROUND OF THE INVENTION.

The present invention relates to a new high-strength silicon steelpossessing improved and unusual combinations of metallurgical andmechanical properties.

It is well known by anyone skilled in the metallurgy of steel thatsilicon is an effective alloying element for increasing strength andtoughness of ferrite and also that the upper limit of silicon forstructural steel is about 2%, since larger amounts cause an unacceptablelowering of toughness.

SUMMARY OF THE INVENTION It is thus a principal object of the presentinvention to obviate the above drawback and to provide a new structuralsteel possessing a high strength and toughness which is characterized inthat Fe-Si alloy containing 46% Si is alloyed witha suitable amount ofMn, Ni and Cr to lower the Ac transformation point to less than 1400"F., thereby preventing the alloy from suifering grain-gross whilesuccessfully imparting toughness thereto.

It is another objectof this invention to provide a new structural steelhaving a high degree of castability and which is well suited for theprecision casting of thin and complex machine parts.

Another object of this invention is to provide a novel structural steelwhich has a high toughness in the as-cast condition.

Still another object of this invention is to provide a new structuralsteel having excellent forging properties and which may be subjected toelectric welding in open air vw'thout preliminary heating.

A further object of this invention is to provide a new structural steelwhich has very high corrosion resistance to various acids.

The product of this invention is characterized by consisting of, byweight: less than 0.03% C, 4-6% -Si, 5l0% Ni, 6-18% Cr, less than 4%each of Mn, Mo and Cu, less than 2% V, the residue being essentially Fe.

It is important that the amount of C, Si, Mn, Ni and Cr be providedWithin the above ranges. For example, the amount of C should not exceedabout 0.03% because more carbon impairs the toughness of the product tosome degree. The amount of Si employed has been found to be mostimportant. When the Si content is less than about 3%, the strength isadversely affected; whereas with Si content above 7%, the toughness isimpaired. For the best combination of strength and toughness, it hasbeen found that the Si content should be within the range of 4% to 6%.

- The total amount of Ni and Mn (Mn is usually held to about 2%) isvaried soas to approach 2 times the Si content, and the Cr varied about2.5 times the Si content, so that the Ac transformation point is loweredto less than 1400 F., thereby preventing the alloy from sufferinggrain-gross, which imparts toughness thereto.

'By using Cu, the corrosion resistance of this alloy to various acidshas been elevated remarkably, especially with respect to sulfuric andhydrochloric acid, while at the same time the forging property islowered. Therefore, it is recommended to add 1-2% Cu for rust-resistingforging and 34% for stainless casting.

For the purposes of deoxidation and refining of austenite grain-size, itis preferable to add less than 1% each of Al, Ti, Cb and B.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order that those skilled inthe metallurgy of steel have a better understanding of the propertieswhich can be obtained by the present invention, the standard compositionranges suitable for certain uses are set forth in the following Table 1.

The characteristics of the high-strength silicon steel according to theinvention are illustrated by the data in Tables 2 and 3, setting forththe mechanical properties of round bars with diameter of 1 inch. Theseround bars have been prepared in such a way that the raw materials aremelted in a high frequency electric furnace in open air to produceingots of 0.5 ton weight which are taken place witha hot-roll to obtainthose round bars.

TABLE 2 Chemical composition of steel A tested, percent :0 0.018, Si4.6, Mn 2.8, Ni 6.6, Cr 10.4, Mo plus V 2.2

Ni CrMo steel Steel A Steel A (4337) Heat treatment Mechanicalproperties:

Hardness, Hv 325 350 350 S., lb./s in 150,000 165, 000 160, 000

Elongation in 2 inch, perc 52. 48. 2 25. 3

R A., percent 68. 3 74. 4 46. 3

Charpy I.V., kg. m./sq. cm..." 28.1 32. 4 16.2

In the above Table 2, the high-strength silicon steel A according to theinvention is compared with the 'NiCrMo structure steel (4337) andcomparing these values of elongation, R.A., Charpy impact value andquality factors. It

will be appreciated that steel A has a very high toughness approximately2 times higher than that of the quench-andtempered NiCrMo steel. On theother hand this data shows that steel A does not have practically anymass-effect on heat-treatment and this enables massive steel forgings,such as rotor-shafts, to have uniform and high strength and toughnesseven over the core thereof.

Table 3 illustrates the mechanical and corrosion-resisting properties ofthe high-strength silicon steel B according to the invention incomparison with those of 18-8 stainless steel (30.4). It will beappreciated that the steel B has overcome the poor resistance of 18-8stainless steel against chlorine and hydrochloric acid and many new usesin the field of chemical industry therefore become possible.

TABLE 3 Chemical composition of steel B tested, percent: 0.022, Si 1.8,Mn 1.8, Ni 7.3, Cr 16.8, Cu 3.4, Mo plus V 1.6

18-8 Stainless Steel In addition to the foregoing mechanical andcorrosionresisting properties, it has been confirmed that thehighstrength silicon steel according to this invention has the followingexcellent characteristics and properties:

(a) It is rich in castability and well adapted for precision casting ofthin and complex machine parts such as turbine blades.

(b) It has excellent forging properties and permits the manufacture of amusic string having a tensile strength of 350,000 lb./s'q. inch and 38turns in twisting.

(c) It has a very high toughness of more than 8 kg. m./sq. cm. of Charpyimpact value in the as-cast condition.

(d) Reduction of toughness is negligible even at temperatures below 32F., and an impact value of "kg. m./sq. cm. may be obtained in liquidnitrogen.

The present invention may be applied to the manufacture of a widevariety of ferrous products and articles T which will be apparent tothose skilled in the metallurgy of steel from the properties of theferrous alloy provided by the invention. These products and articlesinclude machine parts such as reaction vessels for chemical engineering,turbine-discs of jet engines, exhaust valves of internal combustionengines, chassis of cars, bulletproof plates of tanks, protecting coversfor missiles, wire ropes for suspension bridges and marine use, manykinds of springs and various rust-resisting instruments for medical andhome uses.

I claim: 1. A high-strength silicon steel consisting essentially of:

Ingredient: Wt. percent C Less than 0.03. 5 Si 4-6.

Ni 5-10. Cr 6-18 and about 2.5 times Si content. Mn Less than 4.

Mo Do. 10 Cu Do.

V Less than 2. 7 Fe Essentially the remainder. Ni-l-Mn About 2 times Sicontent.

wherein the Ac transformation point of said steel is less than l400 F.

2. A high-strength silicon steel according to claim 1 which alsoincludes less than about 1% of any one of Al, Ti, Cb and B.

3. A high-strength machine structural silicon steel according to claim 1consisting essentially of:

Ingredient: Wt. percent C Up to 0.03. Si 4-5. Mn 1-3.

Mo-i-V' l-3. Cu Up to 1. Fe Essentially the remainder.

4. A high-strength corrosion resisting silicon steel according to claim1 consisting essentially of:

Ingredient: p Wt. percent C Up to 0.03. Si 4.5-5.5.

Mn l-3.

Cr 12-18. Mo-]V 1 3. Cu 1-4. Fe Essentially the remainder.

References Cited UNITED STATES PATENTS 2,747,989 5/ 1956 Kirkby 75-128 C2,839,392 6/1958 Streicher 75-128 3,337,331 8/1967 Ljungberg 75l28 C1,555,395 9/1925 Armstrong -428 3,294,527 12/ 1966 Floreen 75-l23 2,750,283 6/1956 Loveless 75l24 L. DEWAYNE RUTLEDGE, Primary Examiner J. E.LEGR-U, Assistant Examiner US. Cl. XJR.

75l25, 128 C, 128 F, 128G, 128 T, 128 W

